Non-flammable, thermoplastic moulded materials with improved anti-drip properties

ABSTRACT

Flame-retardant, thermoplastic molding materials containing 
     A) at least one polyphenylene ether, 
     B) at least one vinylaromatic polymer and 
     C) at least one flameproofing agent, 
     comprise 
     D) an amount of expandable graphite which increases the resistance of the molding material to dripping 
     and are used for the production of flame-retardant moldings, fibers and films.

The present invention relates to flame-retardant thermoplastic moldingmaterials having improved resistance to dripping, their use for theproduction of fibers, films and moldings, and the fibers, films andmoldings produced therefrom.

Polymer blends comprising polyethylene ether (PPE) and styrene polymersare disclosed, for example, in U.S. Pat. Nos. 3,383,435, 4,128,602 and4,128,603. Such molding materials are suitable for the production ofshaped articles which are distinguished by a better heat distortionresistance compared with high impact polystyrene (HIPS) which is notblended with polyphenylene ethers. A detailed description of theproperties of these polymer blends is also to be found in L.Bottenbruch, Technische Polymer-Blends, Kunststoff Handbuch 3/2, HanserVerlag, Munich, 1993.

An important advantage of the polymer blends comprising a polyphenyleneether and styrene polymers is that molding materials which areflame-retardant and are therefore used for many applications in the areaof electrical engineering can be prepared by adding halogen-freeflameproofing agents, phosphorus-containing compounds being mentioned inparticular. With regard to the use in the area of electricalengineering, in particular the testing of the flame-retardancy accordingto UL 94 (in J. Troitzsch, International Plastics Flammability Handbook,page 346 et seq., Hanser Verlag, Munich, 1990) is critical. In thistest, a flame is repeatedly applied to vertically fastened testspecimens. The test specimen heats up to a very great extent, resultingin many cases in the dripping of burning polymer material which ignitesthe cotton wool pad mounted under the rod. This undesired behavior isobserved particularly when large amounts of flameproofing agents have tobe used to achieve short combustion times.

The problem of the dripping of burning particles in the UL 94 test haslong been known and is solved in the industry generally by adding smallamounts of Teflon as an antidrip agent (U.S. Pat. No. 4,107,232).However, attempts have recently been made completely to avoid the use ofhalogen-containing compounds in thermoplastic molding materials.However, suitable alternative antidrip agents have not been found todate.

EP 0 297 868 discloses the use of expandable graphite in combinationwith carbon black of a certain specification for establishing theconductivity of thermoplastic or heat-curable resins. The resinsobtained according to EP 0 297 888 are suitable in particular for theproduction of electrically conductive materials, such as electrodes, andfor shielding electromagnetic waves. However the problem of improvingthe resistance to dripping is not tackled therein.

JO 3181 532 likewise disclosed the use of expandable graphite forthermoplastic molding materials. However, no flame-retardant moldingmaterials are described therein. The purpose of adding graphiteaccording to JO 3181 532 was to improve the electrical conductivity aswell as the thermal conduction and frictional properties.

It is an object of the present invention to provide flameproofedthermoplastic molding materials, in particular molding materials basedon polyphenylene ethers and styrene polymers, with resistance todripping has been improved by the addition of a halogen-free antidripagent.

We have found that this object is achieved and that, surprisingly, theaddition of an amount of expandable graphite which increases theresistance to dripping, in particular of from about 0.5 to about 10% byweight of expandable graphite, can reduce the dripping offlame-retardant molding materials. According to the invention, it ispossible in particular to obtain molding materials based on PPE and HIPSwhose resistance to dripping has been substantially increased. In thefire test according to UL 94, these novel molding materials can achievethe classification V 0.

This result is all the more surprising since neither EP 0 297 888 nor JO31 81 532 gives any indication that the fire behavior and in particularthe dripping behavior of thermoplastic molding materials, for examplemolding materials comprising polyphenylene ethers and high impactpolystyrene, can be improved simply by means of expanded graphite.

The present invention therefore relates to flame-retardant,thermoplastic molding materials containing a thermoplastic resin basedon one or more polyphenylene ethers and at least one vinylaromaticpolymer, a flameproofing agent and an amount of expandable graphitewhich increases the resistance to dripping of the molding material.Preferably, the expandable graphite is present in an amount of fromabout 0.5 to about 10, preferably from about 0.5 to about 9, inparticular from about 0.5 to about 7.5, % by weight, based on the totalweight of the molding material.

An advantageous embodiment of the invention provides a thermoplastic,flame-retardant molding material which contains, based in each case onthe total weight of the molding material

A) from about 5 to about 97.5% by weight of polyphenylene ether,

B) from about 1 to about 93.5% by weight of styrene polymer,

C) from about 1 to about 20% by weight of flame-proofing agent,

D) from about 0.5 to about 10% by weight of expandable graphite,

E) from about 0 to about 50% by weight of impact modifier and

F) from about 0 to about 60% by weight of conventional additives.

The preferably provided molding material is one which contains, based ineach case on the total weight of the molding material,

A) from about 15 to about 87.5% by weight of polyphenylene ether,

B) from about 10 to about 82.5% by weight of styrene polymer,

C) from about 2 to about 19% by weight of flame-proofing agent,

D) from about 0.5 to about 9% by weight of expandable graphite,

E) from about 0 to about 25% by weight of impact modifier and

F) from about 0 to about 50% by weight of conventional additives.

A particularly preferred molding material is one which contains, basedon the total weight of the molding material,

A) from about 20 to about 82% by weight of polyphenylene ether,

B) from about 15 to about 77% by weight of styrene polymer,

C) from about 2.5 to about 18% by weight of flame-proofing agent,

D) from about 0.5 to 7.5% by weight of expandable graphite,

E) from about 0 to about 20% by weight of impact modifier and

F) from about 0 to about 30% by weight of conventional additives.

According to the invention, at least one polyphenylene ether known perse is used as component A). These are in particular compounds based onsubstituted, in particular disubstituted, polyphenylene ethers, theether oxygen of one unit being bonded to the benzene nucleus of theneighboring unit. Polyphenylene ethers substituted in the 2- and/or6-position relative to the oxygen atom are preferably used. Examples ofsubstituents are halogen, such as chlorine or bromine, and alkyl of 1 to4 carbon atoms which preferably has no a tertiary hydrogen atom, e.g.methyl, ethyl, propyl or butyl. The alkyl radicals may in turn besubstituted by halogen, such as chlorine or bromine, or by hydroxyl.Further examples of possible substituents are alkoxy, preferably of upto 4 carbon atoms, such as methoxy, ethoxy, n-propoxy and n-butoxy, orphenyl which is unsubstituted or substituted by halogen and/or by alkyl.Also suitable are copolymers of various phenols, for example copolymersof 2,6-dimethylphenol and 2,3,6-trimethylphenol. Mixtures of differentpolyphenylene ethers can of course also be used.

Examples of polyphenylene ethers are poly(2,6-dilauryl-1,4-phenyleneether), poly(2,6-diphenyl-1,4-phenylene ether),poly(2,6-dimethoxy-1,4-phenylene ether), poly(2,6-diethoxy-1,4-phenyleneether), poly(2-methoxy-6-ethoxy-1,4-phenylene ether),poly(2-ethyl-6-stearyloxy-1,4-phenylene ether),poly-(2,6-dichloro-1,4-phenylene ether),poly(2-methyl-6-phenyl-1,4-phenylene ether),poly(2,6-dibenzyl-1,4-phenylene ether), poly(2-ethoxy-1,4-phenyleneether), poly-(2-chloro-1,4-phenylene ether) andpoly(2,5-dibromo-1,4-phenylene ether). Preferably used polyphenyleneethers are those in which the substituents are alkyl of 1 to 4 carbonatoms, such as poly(2,6-dimethyl-1,4-phenylene ether),poly(2,6-diethyl-1,4-phenylene ether),poly(2-methyl-6-ethyl-1,4-phenylene ether),poly(2-methyl-6-propyl-1,4-phenylene ether),poly(2,6-dipropyl-1,4-phenylene ether) andpoly(2-ethyl-6-propyl-1,4-phenylene ether).

For the purposes of the present invention, polyphenylene ethers are alsoto be understood as meaning those which are modified with monomers, suchas fumaric acid, maleic acid or maleic anhydride.

Such polyphenylene ethers are described, inter alia, in WO 87/00540.

Regarding the physical properties of the polyphenylene ethers, thosewhich have a weight average molecular weight Mw of from about 8000 toabout 70,000, preferably from about 12,000 to about 60,000, inparticular from about 25,000 to about 50,000, are used in thecompositions. This corresponds to an intrinsic viscosity of about 0.18to about 0.7, preferably from about 0.25 to about 0.62 and in particularfrom about 0.39 to about 0.55 dl/g, measured in chloroform at 25° C.

The molecular weight distribution is determined in general by means ofgel permation chromatography (0.8×50 cm Shodex separation column of thetype A 803, A 804 and A 805 with THF as eluent at room temperature). ThePPE samples are dissolved in THF under pressure at 110° C., 0.16 ml of a0.25% by weight solution being injected. Detection is effected ingeneral using a UV detector. The calibration of the columns was carriedout using PPE samples whose absolute molecular weight distributions weredetermined by a GPC/laser light scattering combination.

The component B) is preferably a toughened vinylaromatic polymer whichis advantageously compatible with the polyphenylene ether used.

Examples of preferred vinylaromatic polymers compatible withpolyphenylene ethers are stated in the monograph by O.Olabisi,Polymer-Polymer Miscibility, 1979, pages 224 to 230 and 245.

Both homopolymers and copolymers of vinylaromatic monomers of 8 to 12carbon atoms, which are prepared in the presence of a rubber, aresuitable. The rubber content is from about 5 to about 25, preferablyfrom about 8 to about 17, % by weight, based on the weight of thecomponent B).

Suitable high impact polystyrenes are for the most part commerciallyavailable and have a viscosity number (VN) of the hard matrix of fromabout 50 to about 130, preferably from about 60 to about 90, ml/g (0.5%strength in toluene at 23° C.).

Particularly suitable monovinylaromatic compounds are styrene and thestyrenes substituted on the nucleus and on the side chain. Preferredsubstituents are halogen, in particular chlorine and bromine, hydroxyl,and C₁₋₄ alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl andtert-butyl. Examples of these compounds are chlorostyrene,a-methylstyrene, styrene, p-methylstyrene, vinyltoluene andp-tert-butylstyrene. However, styrene alone is preferably used.

The homopolymers are generally prepared by the known mass, solution orsuspension processes (cf. Ullmanns Enzyklopädie der techn. Chemie,Volume 19, pages 265 to 272, Verlag Chemie, Weinheim 1980). Thehomopolymers may have weight average molecular weights Mw of from about3000 to about 300,000, which can be determined by conventional methods.

Examples of suitable comonomers for the preparation of copolymers are(meth)acrylic acid, alkyl (meth)acrylates where the alkyl radical is of1 to 4 carbon atoms, acrylonitrile and maleic anhydride as well asmaleimides, acrylamide and methacrylamides and their N,N- orN-alkyl-substituted derivatives in which the alkyl radical is of 1 to 10carbon atoms. Examples of C₁-C₁₀-alkyl radicals include C₁-C₄-alkyl ofthe above definition and n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl,n-decyl and their branched analogs.

The comonomers are contained in the styrene polymers in differentamounts depending on their chemical structure. The miscibility of thecopolymer with the polyphenylene ether is critical with regard to thecontent of comonomers in the copolymer. Such miscibility limits areknown and are described, for example, in U.S. Pat. Nos. 4,360,618 and4,405,753 and in the publication by J. R. Fried and G. A. Hanna, PolymerEng. Sci. 22 (1982), 705 et seq. The copolymers are prepared by knownprocesses which are described, for example, in Ullmanns Enzyklopädie dertechnischen Chemie, Volume 19, page 273 et seq., Verlag Chemie, Weinheim(1980). The copolymers have in general weight average molecular weights(Mw) of from about 10,000 to about 300,000, which can be determined byconventional methods.

The component B) is particularly preferably high impact polystyrene.

The generally used processes for the preparation of high impactpolystyrenes are mass or solution polymerization in the presence of arubber, as described, for example, in U.S. Pat. No. 2,694,692, and masssuspension polymerization processes, as described, for example, in U.S.Pat. No. 2,862,906. Other processes can of course also be used providedthat the desired particle size of the rubber phase is established.

The natural or synthetic rubbers usually used for toughening styrenepolymers are used as the rubber. Suitable rubbers for the purposes ofthe present invention in addition to natural rubber are, for example,polybutadiene, polyisoprene and copolymers of butadiene and/or ofisoprene with styrene and other comonomers, which have a glasstransition temperature, determined according to K. H. Illers and H.Breuer, Kolloidzeitschrift 190 (1) (1963) 16-34, of less than −20° C.According to the invention, mixtures of different toughened polymers ofthe above definition may also be used.

The novel molding materials may contain, as component C), the followingcompounds C1, C2 and C3 individually or as a mixture:

C1) Phosphine oxide of the formula (I)

where R^(a), R^(b) and R^(c) are identical or different and are selectedfrom hydrogen and straight-chain or branched, unsubstituted orsubstituted alkyl, aryl, alkylaryl or cycloalkyl groups of up to 40carbon atoms.

Preferred alkyl radicals here are C₁-C₂₀-alkyl, in particularC₁-C₁₂-alkyl, e.g. methyl, ethyl, n-propyl, n-butyl, neopentyl, n-hexyl,n-octyl, n-nonyl, n-dodecyl, 2-ethylhexyl, 3,5,5-tri-methylhexyl andsubstituted alkyl radicals, such as cyanoethyl.

Preferred aryl radicals are phenyl and naphthyl as well asmonosubstituted or polysubstituted radicals, such as tolyl, xylyl,mesityl and cresyl.

Preferred alkylaryl radicals are C₁-C₂₀-alkylaryl, in particularC₁-C₁₂-alkylaryl, the alkyl moiety and aryl moiety being as definedabove.

Preferred cycloalkyl groups include C₃-C₁₀-cycloalkyl, such ascyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl.

Suitable substituents are cyano, hydroxy, C₁-C₄-alkyl and halogen, suchas F, Cl, Br and I.

C2) Phosphate of the formula (II)

in which the substituents R^(a), R^(b) and R^(c) are identical ordifferent and have the abovementioned meanings, and

C3) a boron compound.

Examples of phosphine oxides C1) are triphenylphosphine oxide,tritolylphosphine oxide, trisnonylphenylphosphine oxide,tricyclohexylphosphine oxide, tris(n-butyl)phosphine oxide,tris(n-hexyl)phosphine oxide, tris(n-octyl)phosphine oxide,tris(cyanoethyl)phosphine oxide, benzylbis(cyclohexyl)phosphine oxide,benzylbisphenylphosphine oxide and phenylbis(n-hexyl)-phosphine oxide.Triphenylphosphine oxide, tricyclohexylphosphine oxide,tris(n-octyl)phosine oxide and tris(cyanoethyl)phosphine oxide areparticularly preferably used.

Particularly suitable phosphates C2) are alkyl- and aryl-substitutedphosphates. Examples are phenyl bisdodecyl phosphate, phenylbisneopentyl phosphate, phenyl ethyl hydrogen phosphate, phenylbis(3,5,5-trimethylhexyl) phosphate, ethyl diphenyl phosphate,bis(2-ethylhexyl) p-tolyl phosphate, tritolyl phosphate, trixylylphosphate, trimesityl phosphate, bis(2-ethylhexyl) phenyl phosphate,tris(nonylphenyl) phosphate, bis(dodecyl) p-tolyl phosphate, tricresylphosphate, triphenyl phosphate, dibutyl phenyl phosphate, p-tolylbis(2,5,5-trimethylhexyl) phosphate and 2-ethylhexyl diphenyl phosphate.Phosphorus compounds in which each of the radicals R^(a), R^(b) andR^(c) is an aryl radical are particularly suitable. Triphenyl phosphate,trixylyl phosphate and trimesityl phosphate are very particularlysuitable. Cyclic phosphates may also be used. Particularly suitable hereis diphenyl pentaerythrityl diphosphate.

Particularly preferred mixtures of the following phosphine oxide C1) andphosphate C2) combinations are: triphenylphosphine oxide/triphenylphosphate or trixylyl phosphate, tricyclohexylphosphine oxide andtriphenyl phosphate, tris(cyanoethyl)phosphine oxide and triphenylphosphate, and tris(n-octyl)phosphine oxide and triphenyl phosphate.Mixtures of a plurality of phosphine oxides and phosphates may also beused, for example the mixture comprising triphenylphosphine oxide,triphenyl phosphate and trixylyl phosphate.

The molecular weight is in general not more than about 1000, preferablyfrom about 150 to about 800.

According to the invention, boron compounds C3) are to be understood asmeaning both inorganic and organic boron compounds.

Examples of inorganic boron compounds are boric acid, B₂O₃ and salts ofboric acid, preferably with alkali metals or alkaline earth metals.Boric acid, sodium borate and boron oxide are particularly preferred.

Organic boron compounds C3) are, for example, tetraphenyl borates, suchas sodium tetraphenylborate, and tribenzyl borate.

In the case of a mixture of C1, C2 and C3, the composition of thecomponent C) is in general, based on the content of the total componentC):

C1) from 1 to 98.9, preferably from 10 to 85, in particular from 20 to70, % by weight

C2) from 1 to 98.9, preferably from 10 to 85, in particular from 20 to70, % by weight

C3) from 0.1 to 70, preferably from 5 to 50, in particular from 10 to30, % by weight.

Other suitable components C) are organophosphorus compounds of theformulae (IV), (V) and (VI)

where

R¹ and R⁴, independently of one another, are each unsubstituted orsubstituted alkyl or aryl;

R², R³, R⁷ and R⁸, independently of one another, are each unsubstitutedor substituted alkyl, aryl, alkoxy or aryloxy,

R⁵ is alkylene, —SO₂—, —CO—, —N═N— or —(R⁶)P(O)—, where R⁶ isunsubstituted or substituted alkyl, aryl or alkylaryl, and n and p,independently of one another, are each from 1 to 30.

Suitable substituents in compounds of the formulae (IV), (V) and (VI)are cyano, hydroxyl, C₁-C₄-alkyl and halogen, such as F, Cl, Br or I.

Preferred alkyl radicals in compounds of the formula (IV), (V) and (VI)are C₁-C₂₀-alkyl, in particular C₁-C₁₂-alkyl, e.g. methyl, ethyl,n-propyl, n-butyl, neopentyl, n-hexyl, n-octyl, n-nonyl, n-dodecyl,2-ethylhexyl, 3,5,5-trimethylhexyl and cyanoethyl.

Preferred aryl radicals in compounds of the formulae (IV), (V) and (VI)are phenyl and naphthyl and monosubstituted or polysubstituted radicals,such as tolyl, xylyl, mesityl and cresyl.

Preferred alkylaryl radicals in compounds of the formulae (IV), (V) and(VI) are C₁-C₂₀-alkylaryl, in particular C₁-C₁₂-alkylaryl, the alkylmoiety and aryl moiety being as defined above.

Preferred cycloalkyl groups in compounds of the formulae (IV), (V) and(VI) include C₃-C₁₀-cycloalkyl, such as cyclobutyl, cyclopentyl,cyclohexyl and cycloheptyl.

Preferred alkoxy radicals in compounds of the formulae (IV), (V) and(VI) are C₁-C₂₀-alkoxy, the C₁-C₂₀-alkyl moiety being as defined above.

Preferred aryloxy radicals in compounds of the formulae (IV), (V) and(VI) are those in which the aryl moiety is as defined above.

Preferred alkylene radicals in compounds of the formulae (IV), (V) and(VI) are C₁-C₆-alkylene, such as methylene, ethylene, propylene andhexylene.

The preparation of phosphoric esters is generally described inHouben-Weyl, Methoden der organischen Chemie, vol. XII/2, Thieme Verlag,1972. The compounds used according to the invention are preferablyobtained by transesterification under base catalysis or by reaction ofphosphoryl chloride with phenols under catalysis by magnesium chlorideor aluminum chloride. Preferred compounds of the formula (IV) are thecommercial products based on hydroquinone diphenyl phosphate orresorcinol diphenyl phosphate. Preferred compounds of the formula (V)are obtained by reacting a bisphenol (cf. for example Ullmann'sEncyclopedia of Industrial Chemistry, 5th edition, vol. A19, page 349),e.g. bisphenol A or S, with triphenyl phosphate under base catalysis.

In this context, it should be noted that the industrially availableproducts are mixtures of different oligomers or isomers.

Furthermore, mixtures of the higher phosphates and monophosphates ormonophosphine oxides in any ratio may be used.

The molding materials contain expandable graphite as component D).

As is known to the person skilled in the art, graphite can formintercalation compounds owing to its layer structure (also cf.: Römpp,Chemie-Lexikon, 9th edition, vol. 2, page 1642 et seq., Thieme-Verlag,Stuttgart, 1990).

The intercalated component is included in a regular manner between thelayers of the graphite. On intercalation of the component, expansion ofthe graphite in the direction of c axis also takes place. Thisintercalation is generally reversible, i.e. liberation of theintercalated component is possible at higher temperatures. Particularlysuitable intercalation compounds contain at least about 10% by weight ofinert compounds which are liberated at a temperature of at least about240° C., preferably more than about 250° C. Suitable inert compoundsare, for example, water, carbon dioxide, sulfide trioxide and nitrogen.

The preparation of such intercalation compounds is known to a personskilled in the art. For the preparation of intercalation compounds,graphite powder is treated with the gaseous or liquid component underpressure (cf. Ullmann's Encyclopedia of Industrial Chemistry, A5, 1986,page 99 et seq. and page 122 et seq.). On heating, the intercalatedcompound is liberated, it being possible for the volume to increase by afactor of 200 (cf. product publication Expandable Graphite from ChuoKasei Co., Ltd.).

Rubber impact modifiers are preferably used as component E).

In addition to the rubber-containing component B, natural or syntheticrubbers may be used as component E. In addition to natural rubber, othersuitable impact modifiers are, for example, polybutadiene, polyisopreneor copolymers of butadiene and/or isoprene with styrene and othercomonomers, which have a glass transition temperature, determinedaccording to K. H. Illers and H. Breuer, Kolloidzeitschrift 190 (1)(1963), 16-34, of from about −100° C. to +25° C., preferably less than0° C. Appropriately hydrogenated products may also be used.

Preferred impact modifiers E are block copolymers of vinylaromatics anddienes. Impact modifiers of this type are known. German PublishedApplications DE-AS 1,932,234 and DE-AS 2,000,118 and German Laid-OpenApplication DOS 2,255,930 describe vinylaromatic and elastomeric blockcopolymers comprising diene blocks and having different compositions.The use of corresponding hydrogenated block copolymers, if necessary asa mixture with the nonhydrogenated precursor, as impact modifiers isdescribed, for example, in German Laid-Open Applications DOS 2,750,515,DOS 2,434,848 and DOS 3,038,551, EP-A-0 080 666 and WO 83/01254.

In particular, vinylaromatic/diene block copolymers comprising blockswhich contain a hard phase (block type S) and, as the soft phase, ablock B/S comprising diene and vinylaromatic units and having a randomcomposition can be used according to the invention. The composition canbe homogeneous or inhomogeneous along the chain as a statisticalaverage.

Such an elastomeric block copolymer suitable according to the inventionis obtained by forming the soft phase from a random copolymer of avinylaromatic with a diene; random copolymers of vinylaromatics anddienes are obtained by polymerization in the presence of a polarcosolvent.

A block copolymer which can be used according to the invention may be,for example, of one of the following formulae (1) to (11):

(1) (S-B/S)_(n);

(2) (S-B/S)_(n)-S;

(3) B/S-(S-B/S)_(n);

(4) X-[(S-B/S)_(n)]_(m)+1

(5) X-[(B/S-S)_(n)]_(m)+1;

(6) X-[(S-B/S)_(n)-S]_(m)+1;

(7) X-[(B/S-S)_(n)-B/S]_(m)+1;

(8) Y-[(S-B/S)_(n)]_(m)+1;

(9) Y-[(B/S-S)_(n)]_(m)+1;

(10) Y-[(S-B/S)_(n)-S]_(m)+1;

(11) Y-[(B/S-S)_(n)-B/S]_(m)+1;

where

S is a vinylaromatic block,

B/S is the soft phase comprising a block randomly composed of diene andvinylaromatic units,

X is a radical of an n-functional initiator,

Y is a radical of an m-functional coupling agent and

m, n are natural numbers from 1 to 10.

A block copolymer of one of the formulae S-B/S-S, X-[-B/S-S]₂ andY-[-B/S-S]₂ (meanings of the abbreviations as above) is preferred and ablock copolymer whose soft phase is divided into the blocks

(12) (B/S)₁-(B/S)₂;

(13) (B/S)₁-(B/S)₂-(B/S)₁;

(14) (B/S)₁-(B/S)₂-(B/S)₃;

is particularly preferred, the indices 1, 2, 3 representing differentstructures in the sense that the vinylaromatic/diene ratio is differentin the individual blocks B/S or changes continuously within the limits(B/S)₁(B/S)₂ within a block, and the glass transition temperature T_(g)of each part-block being less than 25° C.

A block copolymer which has a plurality of blocks B/S and/or S having adifferent molecular weight for each molecule is also preferred.

Furthermore, block S composed exclusively of vinylaromatic units can bereplaced by a block B, since all that is important is that anelastomeric block copolymer is formed. Such copolymers can have, forexample, one of the structures (15) to (18)

(15) B-(B/S)

(16) (B/S)-B-(B/S)

(17) (B/S)₁-B-(B/S)₂

(18) B-(B/S)₁-(B/S)₂.

Preferred vinylaromatics are styrene, o-methylstyrene, vinyltoluene andmixtures of these compounds. Preferred dienes are butadiene, isoprene,piperylene, 1-phenylbutadiene and mixtures of these compounds. Aparticularly preferred monomer combination comprises butadiene andstyrene.

The soft blocks are particularly preferably composed of from about 25 to75% by weight of styrene and from about 25 to 75% by weight ofbutadiene.

Particularly preferred soft blocks are those which have a butadienecontent of from about 34 to 69% by weight and a styrene content of fromabout 31 to 66% by weight.

In the case of the styrene/butadiene monomer combination, the amount byweight of the diene in the total block copolymer is from 15 to 65% byweight and that of the vinylaromatic component is accordingly from 85 to35% by weight. Butadiene/styrene block copolymers having a monomercomposition comprising from 25 to 60% by weight of diene and from 75 to40% by weight of vinylaromatic compound are particularly preferred.

The block copolymers are obtainable by anionic polymerization in anonpolar solvent with the addition of a polar cosolvent. It isconsidered that the cosolvent acts as a Lewis base with respect to themetal cation. Aliphatic hydrocarbons, such as cyclohexane ormethylcyclohexane, are preferably used as solvents. Polar aproticcompounds, such as ethers and tertiary amines, are preferred as Lewisbases. Examples of particularly effective ethers are tetrahydrofuran andaliphatic polyethers, such as diethylene glycol dimethyl ether. Examplesof tertiary amines are tributylamine and pyridine. The polar cosolventis added to the nonpolar solvent in a small amount, for example from 0.5to 5% by volume. Tetrahydrofuran in an amount of from 0.1 to 0.3% byvolume is particularly preferred. Experience has shown that an amount ofabout 0.2% by volume is sufficient in most cases.

The copolymerization parameters and the proportion of 1,2- and1,4-linkages of the diene units are determined by the dose and structureof the Lewis base. The novel polymers contain, for example, from 15 to40% of 1,2-linkages and from 85 to 60% of 1,4-linkages, based on alldiene units.

The anionic polymerization is initiated by means of organo-metalliccompounds. Compounds of the alkali metals, in particular of lithium, arepreferred. Examples of initiators are methyllithium, ethyllithium,propyllithium, n-butyllithium, sec-butyllithium and tert-butyllithium.The organometallic compound is added as a solution in a chemically inerthydrocarbon. The dose depends on the intended molecular weight of thepolymer but is as a rule from 0.002 to 5 mol %, based on the monomers.

The polymerization temperature may be from about 0 to 130° C. Thetemperature range from 30 to 100° C. is preferred.

The volume fraction of the soft phase in the solid is of decisiveimportance with regard to the mechanical properties. According to theinvention, the volume fraction of the soft phase composed of diene andvinylaromatic sequences is from 60 to 95, preferably from 70 to 90,particularly preferably from 80 to 90, % by volume. The blocks A formedfrom the vinylaromatic monomers constitute the hard phase whose volumefraction is accordingly from 1 to 40, preferably from 10 to 30,particularly preferably from 10 to 20, % by volume.

It should be pointed out that there is no stringent agreement betweenthe abovementioned ratios of vinylaromactic compound and diene, theabovementioned limits of the phase volumes and the composition whicharises out of the glass transition temperature ranges according to theinvention, since the numerical values in question have been rounded tofull units of ten. Any agreement is likely to be accidental.

The volume fraction of the two phases can be measured by means ofhigh-contrast electron microscopy or solid-state NMR spectroscopy. Theproportion of the vinylaromatic blocks can be determined byprecipitation and weighing after osmium degradation of the polydienefraction. The future phase ratio of a polymer can also be calculatedfrom the amounts of monomers used if polymerization is allowed to go tocompletion each time.

The block copolymer is uniquely defined for the purposes of the presentinvention by the quotient of the volume fraction in percent of the softphase formed from the B/S block and the fraction of diene units in thesoft phase, which is from 25 to 70% by weight for the combinationstyrene/butadiene.

The glass transition temperature (T_(g)) is influenced by the randomincorporation of the vinylaromatic compounds into the soft block of theblock copolymer and the use of Lewis bases during the polymerization.The glass transition temperature of the total copolymer is preferablyfrom −50 to +25° C., preferably less than 0° C.

The molecular weight of the block S is preferably from 1000 to 200,000,in particular from 3000 to 80,000 [g/mol]. Within a molecule, S blocksmay have different molar masses.

The molecular weight of the block B/S is usually from 2000 to 45250,000, preferably from 5000 to 150,000 [g/mol].

Like block S, block B/S, too, can have different molecular weight valueswithin a molecule.

The coupling center X is formed by the reaction of the living anionicchain ends with a bifunctional or polyfunctional coupling agent.Examples of such compounds are to be found in U.S. Pat. Nos. 3,985,830,3,280,084, 3,637,554 and 4,091,053. For example, epoxidized glycerides,such as epoxidized linseed oil or soybean oil, are preferably used;divinylbenzene is also suitable. Dichlorodialkylsilanes, dialdehydes,such as terephthalaldehyde, and esters, such as ethylformate orbenzoate, are especially suitable for dimerization.

Preferred polymer structures are S-B/S-S, X-[-B/S-S]₂ and Y-[-B/S-S]₂,where the random block B/S itself can in turn be subdivided into blocksB1/S1-B2/S2-B3/S3- . . . Preferably, the random block consists of from 2to 15 random part-blocks, particularly preferably of from 3 to 10part-blocks. The division of the random block B/S into as manypart-blocks Bn/Sn as possible has a decisive advantage that, even in thecase of a composition gradient within a part-block Bn/Sn, as isdifficult to avoid in the anionic polymerization under practicalconditions, the B/S block as a whole behaves like a virtually perfectrandom polymer. It is therefore possible to add less than thetheoretical amount of Lewis base, which increases the proportion of1,4-diene linkages, decreases the glass transition temperature T_(g) andreduces the susceptibility of the polymer to crosslinking. A larger or asmaller amount of part-blocks can be provided with a high diene content.As a result of this, the polymer retains a residual toughness and doesnot become completely brittle, even below the glass transitiontemperature of the predominant B/S blocks.

All abovementioned weight and volume data are based on the monomercombination butadiene/styrene. However, these data can be directlyconverted for other monomers technically equivalent to styrene andbutadiene.

The block copolymers can be worked up by protonating the carbanions withan alcohol, such as isopropanol, acidifying the reaction mixture, forexample, with a mixture of CO₂ and water, and removing the solvent. Theblock copolymers may contain antioxidants and antiblocking agents.

Mixtures of the above rubbers may also be used in the novel moldingmaterials.

The novel molding materials may, if required, contain conventionaladditives and processing assistants as component F).

Examples of suitable additives are heat stabilizers and lightstabilizers, lubricants and mold release agents, colorants, such as dyesand pigments, in conventional amounts. Further additives are reinforcingmaterials, such as glass fibers, asbestos fibers, carbon fibers,aromatic polyamide fibers and/or fillers, such as gypsum fibers,synthetic calcium silicates, kaolin, calcined kaolin, wollastonite, talcand chalk.

Low molecular weight or high molecular weight polymers are also suitableas additives, polyethylene wax being particularly preferred aslubricant.

Examples of suitable pigments are TiO₂ and carbon blacks.

When TiO₂ is used, the mean particle size is from about 50 to 400 nm, inparticular from about 150 to 240 nm. Rutiles and anatase are usedindustrially and may be coated with metal oxides, for example aluminumoxide, silicon oxides, zinc oxides or siloxanes.

Carbon blacks include microcrystalline, finely divided carbon (cf.Kunststofflexikon, 7th edition 1980). Furnace blacks, acetylene blacks,gas blacks and the thermal carbon blacks obtainable by thermalpreparation are suitable. The particle sizes are preferably from about0.01 to 0.1 μm and the surface areas from about 10² to 10⁴ m²/g(BET/ASTM D 3037), and from about 10² to 10³ ml/l00 g in the case of DBPabsorption (BET/ASTM d 2414).

The desired properties of the end products can be controlled to a largedegree through the type and amount of these additives.

The novel molding materials are advantageously prepared by mixing thecomponents at from 230 to 320° C. in a conventional mixing apparatus,for example a kneader, a Banbury mixer or a single-screw extruder,preferably with a twin-extruder extruder, but it should be noted thatthe processing must be carried out below the temperature at whichliberation of the inert compound takes place. Thorough mixing isnecessary to obtain a very homogeneous molding material. The order inwhich the components are mixed may be varied; two, or if required, aplurality of components may be premixed or all components may be mixedtogether.

Moldings which are flame-retardant and do not tend to drip burningparticles in the fire test according to UL 94 can be produced from thenovel molding materials, for example by injection molding or extrusion.

The novel molding materials are very suitable for the production ofshaped articles of all types, for example by injection molding orextrusion. They may furthermore be used for the production of films andsemifinished products by the thermalforming or blow molding method.

EXAMPLES

The novel molding materials 1, 2 and 3 and, for comparative purposes,the molding materials V1 and V2 are prepared using the components A) toF) mentioned below and are tested.

Component A)

Poly-2,6-dimethyl-1,4-phenylene ether having an average molecular weight(M_(W)) of 40,000 g/mol.

Component B₁)

High impact polystyrene containing 9% by weight of polybutadiene andhaving cellular particle morphology and a mean particle size of the softcomponent of 1.9 μm. The VZ of the hard matrix was 80 ml/g (0.5%strength in toluene at 23° C.).

Component B₂)

High impact polystyrene containing 11% by weight of polybutadiene andhaving cellular particle morphology and a mean particle size of the softcomponent of 3.5 μm. The VZ of the hard matrix was 80 ml/g (0.5%strength in toluene at 23° C.).

Component C)

Resorcinol diphosphate, e.g. Fyroflex RDP (Akzo).

Component D)

Expandable graphite, e.g. Sigraflex FR 90-60/80.

Component E)

SEBS block rubber Kraton G 1650 (Shell AG).

Component F)

Black Pearls 880 carbon black (as 15% strength batch in polystyrene, VZ=80 ml/g 0.5% strength in toluene at 23° C.).

Preparation of the thermoplastic molding material

The components A) to F) were mixed in a twin-screw extruder (ZKS 30 fromWerner & Pfleiderer) at 240° C., the mixture was extruded and theextrudate was cooled and granulated.

The dried granules were processed at from 240 to 260° C. to givecircular disks, flat bars for the UL 94 test and standard small bars.

The damaging energy WS was determined according to DIN 53 443 at 23° C.The heat distortion resistance of the samples was determined by means ofthe Vicat softening temperature, measured according to DIN 53 460 with aforce of 49.05 N and a temperature increase of 50 K per hour, usingstandard small bars.

The flame retardancy and the dripping behavior were determined accordingto UL 94 on {fraction (1/16)}″ thick bars; the combustion timesmentioned are the sum of the combustion times of two flame applications.

The compositions and properties of the thermoplastic molding materialsare listed in Table 1.

TABLE 1 Molding material No. V1 1 2 V2 3 Component [% by weight] A 4039,1 38,3 32 30,5 B₁ 47 46.0 44.9 44.2 42.0 B₂ — — — 2.5 2.4 C 10 10 1214 14 D — 2 2 — 4 E 3 2,9 2.8 4 3.8 F — — — 3.3 3.3 W_(s) [Nm] 34 28 2924 23 Vicat B [° C.] 111 110 108 94 91 UL 94 V-2 V-1 V-O V-2 V-1Combustion time [s] 74 76 42 154 89 Bars dripped 5 0 0 5 0

The tests demonstrate the surprisingly high efficiency of component D)as antidrip agent.

We claim:
 1. A flame-retardant, thermoplastic molding materialcontaining A) at least on e polyphenylene ether, B) at least onevinylaromatic polymer and C) at least one flameproofimg agent other thanred phosphorus, wherein said molding material furthermore comprises D)an amount of expandable graphite which increases the resistance of themolding material to dripping.
 2. A molding material as claimed in claim1, wherein the expandable graphite is present in an amount of from about0.5 to about 10% by weight.
 3. A molding material as claimed in claim 2,containing, based in each case on the total weight of the moldingmaterial, A) from about 5 to about 97.5% by weight of polyphenyleneether, B) from about 1 to about 93.5% by weight of styrene polymer, C)from about 1 to about 20% by weight of flameproofing agent, D) fromabout 0.5 to about 10% by weight of expandable graphite, E) from about 0to about 50% by weight of impact modifier and F) from about 0 to about60% by weight of conventional additives.
 4. A thermoplastic moldingmaterial as claimed in claim 1, wherein component D) is an intercalationcompound comprising graphite and an inert compound, the liberation ofwhich takes place at above about 240° C. at about atmospheric pressure.5. A thermoplastic molding material as claimed in claim 4, the amount ofthe inert compound being at least 10% by weight, based on component D).6. A thermoplastic molding material as claimed in claim 5, the inertcompound being selected from H₂O, CO₂, SO₃ or N₂.
 7. A thermoplasticmolding material as claimed in claim 1, wherein the flameproofing agentused is resorcinol diphenyl phosphate or hydroquinone diphenylphosphate.
 8. A flame-retardant molding, fiber or film produced using amolding material as claimed in any of claims 1 to 7.